AP Physics 1: Algebra-Based, AP exams, 10–15%

Unit 5: Torque and Rotational Dynamics

Unit 5 rebuilds kinematics and dynamics for rotation. Angular position, velocity, and acceleration parallel their linear counterparts, torque replaces force, and rotational inertia replaces mass. The strongest approach is to learn each rotational idea alongside its translational analogue rather than as a separate topic.

Position: 5 of 8 units
Published weighting: 10–15% in the official framework
Topics covered: 6 topics in this guide

What is covered

Topics inside this unit.

These topics describe the scope students most often review for this part of AP Physics 1: Algebra-Based. Treat them as a study checklist rather than an exhaustive list of what a single exam form can sample.

Rotational kinematics: Angular displacement, velocity, and acceleration, and the equations that mirror the linear case.
Connecting linear and rotational motion: Relating arc length, tangential speed, and tangential acceleration to their angular counterparts.
Torque: Torque as force times lever arm, the role of the angle of application, and the sign convention for rotation.
Rotational inertia: How mass distribution relative to the axis determines resistance to angular acceleration.
Rotational equilibrium: Balanced torques and balanced forces, and analyzing beams, levers, and supported bars.
Newton's second law in rotational form: Net torque as the product of rotational inertia and angular acceleration, applied to rigid bodies.

Study tips

How to practice Torque and Rotation.

Section-specific guidance that follows from how this material is usually tested.

Keep a two-column table pairing each translational quantity with its rotational analogue and update it as the unit proceeds.
Practice choosing the pivot deliberately in equilibrium problems; a good choice removes unknowns.
Draw the lever arm explicitly rather than estimating it from the diagram.

Where this fits

Unit 5: Torque and Rotational Dynamics is 5 of 8 units in the AP Physics 1: Algebra-Based guide, and it carries a published weighting of 10–15% in the official framework. Use the full guide to balance it against everything else you have to review.

Back to the AP Physics 1: Algebra-Based guide Official exam information

Sample Torque and Rotation questions

Practice questions, not yet expert-reviewed

Original practice questions written to the published framework for this section. No expert has reviewed them, and they are not taken from any official exam. Try each one before you open the answer.

Question 1Foundational
A mechanic applies a 20 N force perpendicular to a wrench handle at a point 0.30 m from the bolt at the center of rotation. What is the magnitude of the torque about the bolt?
1. A0.015 N m
2. B3.0 N m
3. C6.0 N m
4. D60 N m
Show answer
Answer: C. 6.0 N m
For a force applied perpendicular to the lever arm, torque is simply the product: (20 N)(0.30 m) = 6.0 N m. The 60 N m choice misplaces the decimal in the distance, and 0.015 N m divides instead of multiplying.
Key insight: Torque depends on both the force and how far from the axis it acts, which is why a longer wrench turns a stubborn bolt.
Question 2Foundational
A uniform meter stick is balanced on a pivot at its center. A 4.0 N weight hangs 0.20 m to the left of the pivot. At what distance to the right of the pivot must a 2.0 N weight hang so that the stick stays balanced?
1. A0.10 m
2. B0.20 m
3. C0.40 m
4. D0.80 m
Show answer
Answer: C. 0.40 m
Balanced torques require (4.0 N)(0.20 m) = (2.0 N)d, so d = 0.80/2.0 = 0.40 m. The 0.10 m choice inverts the ratio, placing the lighter weight closer to the pivot rather than farther away.
Key insight: To balance a lever, a smaller force needs a proportionally longer lever arm.
Question 3Intermediate
A wheel with rotational inertia 0.50 kg m^2 about its axle experiences a net torque of 2.0 N m. What is the magnitude of its angular acceleration?
1. A0.25 rad/s^2
2. B1.0 rad/s^2
3. C2.5 rad/s^2
4. D4.0 rad/s^2
Show answer
Answer: D. 4.0 rad/s^2
The rotational form of Newton's second law gives alpha = torque / I = 2.0 N m / 0.50 kg m^2 = 4.0 rad/s^2. The 1.0 rad/s^2 choice multiplies torque by rotational inertia instead of dividing.
Key insight: Rotational inertia plays the role of mass in rotation: the same torque spins up a low-inertia wheel faster.
Question 4Intermediate
A disk starts from rest and undergoes a constant angular acceleration of 3.0 rad/s^2 for 4.0 s. Through what angle does the disk turn during that time?
1. A6.0 rad
2. B12 rad
3. C24 rad
4. D48 rad
Show answer
Answer: C. 24 rad
Rotational kinematics mirrors the linear case: theta = (1/2)(alpha)t^2 = (1/2)(3.0)(4.0)^2 = 24 rad. The 12 rad choice is the final angular velocity of 12 rad/s mistaken for an angle, and 48 rad omits the factor of one half.
Key insight: Every constant-acceleration equation has a rotational twin with theta, omega, and alpha in place of x, v, and a.
Question 5Advanced
A uniform 6.0 m beam weighing 200 N rests horizontally on two supports, one at each end. A person weighing 400 N stands 1.5 m from the left end. What is the magnitude of the upward force the left support exerts on the beam?
1. A200 N
2. B300 N
3. C400 N
4. D500 N
Show answer
Answer: C. 400 N
Taking torques about the right support, the left force satisfies N(6.0 m) = (200 N)(3.0 m) + (400 N)(4.5 m) = 2400 N m, so N = 400 N. The remaining 200 N of the 600 N total load is carried by the right support, which confirms the vertical force balance.
Key insight: Choosing the pivot at one unknown force removes it from the torque equation and leaves a single unknown.

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Unit 5: Torque and Rotational Dynamics